The word prognatus as written on the Sarcophagus of Lucius Cornelius Scipio Barbatus (280 BC) reveals the full development of the Latin R by that time; the letter P at the same time still retains its archaic shape distinguishing it from Greek or Old Italic rho.

The original Semitic letter may have been inspired by an Egyptian hieroglyph for tp, "head".[citation needed] It was used for /r/ by Semites because in their language, the word for "head" was rêš (also the name of the letter). It developed into Greek 'Ρ' ῥῶ (rhô) and Latin R.

The descending diagonal stroke develops as a graphic variant in some Western Greek alphabets (writing rho as ), but it was not adopted in most Old Italic alphabets; most Old Italic alphabets show variants of their rho between a "P" and a "D" shape, but without the Western Greek descending stroke.
Indeed, the oldest known forms of the Latin alphabet itself of the 7th to 6th centuries BC, in the Duenos and the Forum inscription, still write r using the "P" shape of the letter.
The Lapis Satricanus inscription shows the form of the Latin alphabet around 500 BC. Here, the rounded, closing Π shape of the p and the Ρ shape of the r have become difficult to distinguish.
The descending stroke of the Latin letter R has fully developed by the 3rd century BC, as seen in the Tomb of the Scipios sarcophagus inscriptions of that era. From around 50 AD, the letter P would be written with its loop fully closed, assuming the shape formerly taken by R.

The minuscule (lowercase) form (r) developed through several variations on the capital form.
Along with Latin minuscule writing in general, it developed ultimately from Roman cursive via the uncial script of Late Antiquity into the Carolingian minuscule of the 9th century.

In handwriting, it was common not to close the bottom of the loop but continue into the leg, saving an extra pen stroke. The loop-leg stroke shortened into the simple arc used in the Carolingian minuscule and until today.

A calligraphic minuscule r, known as r rotunda (ꝛ), was used in the sequence or, bending the shape of the r to accommodate the bulge of the o (as in oꝛ as opposed to or). Later, the same variant was also used where r followed other lower case letters with a rounded loop towards the right (such as b, h, p) and to write the geminate rr (as ꝛꝛ). Use of r rotunda was mostly tied to blackletter typefaces, and the glyph fell out of use along with blackletter fonts in English language contexts mostly by the 18th century.

Insular script used a minuscule which retained two downward strokes, but which did not close the loop ("Insular r", ꞃ); this variant survives in the Gaelic type popular in Ireland until the mid-20th century (but now mostly limited to decorative purposes).

The name of the letter in Latin was er (/ɛr/), following the pattern of other letters representing continuants, such as F, L, M, N and S. This name is preserved in French and many other languages. In Middle English, the name of the letter changed from /ɛr/ to /ar/, following a pattern exhibited in many other words such as farm (compare French ferme), and star (compare German Stern).

The letter R is sometimes referred to as the littera canina (canine letter). This phrase has Latin origins: the Latin R was trilled to sound like a growling dog. A good example of a trilling R is the Spanish word for dog, perro.[4]

The letter ⟨r⟩ is the eighth most common letter in English and the fourth-most common consonant (after ⟨t⟩, ⟨n⟩, and ⟨s⟩).[6]

The letter ⟨r⟩ is used to form the ending "-re", which is used in certain words such as centre in some varieties of English spelling, such as British English. Canadian English also uses the "-re" ending, unlike American English, where the ending is usually replaced by "-er" (center). This does not affect pronunciation.

German stage standard; some Dutch dialects (in Brabant and Limburg, and some city dialects in The Netherlands), Swedish in Southern Sweden, Norwegian in western and southern parts, Venetian only in Venice area.

Other languages may use the letter ⟨r⟩ in their alphabets (or Latin transliterations schemes) to represent rhotic consonants different from the alveolar trill. In Haitian Creole, it represents a sound so weak that it is often written interchangeably with ⟨w⟩, e.g. 'Kweyol' for 'Kreyol'.

Brazilian Portuguese has a great number of allophones of /ʁ/ such as [χ], [h], [ɦ], [x], [ɣ], [ɹ] and [r], the latter three ones can be used only in certain contexts ([ɣ] and [r] as ⟨rr⟩; [ɹ] in the syllable coda, as an allophone of /ɾ/ according to the European Portuguese norm and /ʁ/ according to the Brazilian Portuguese norm). Usually at least two of them are present in a single dialect, such as Rio de Janeiro's [ʁ], [χ], [ɦ] and, for a few speakers, [ɣ].